class Solution:
    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
        if not matrix or not matrix[0]:
            return []
        left=0
        right=len(matrix[0])-1
        top=0
        bottom=len(matrix)-1
        order=[]
        while left <= right and top <= bottom:
            for column in range(left, right + 1):
                order.append(matrix[top][column])
            for row in range(top + 1, bottom + 1):
                order.append(matrix[row][right])
            if left < right and top < bottom:
                for column in range(right - 1, left, -1):
                    order.append(matrix[bottom][column])
                for row in range(bottom, top, -1):
                    order.append(matrix[row][left])
            left, right, top, bottom = left + 1, right - 1, top + 1, bottom - 1
        return order

